1. Field of the Invention
The present invention relates to a lock device which operates a mechanism to be operated such as a locking mechanism or the like which is the object of key operation by a key inserted in a key insertion hole, and which maintains the mechanism to be operated in a non-operating state.
2. Description of the Related Art
The structure disclosed in Japanese Patent Application Laid-Open (JP-A) No. 5-59849 is known as an example of a lock device provided at the door or the like of an automobile. This lock device has: a key cylinder provided rotatably within an accommodating hole of a cylindrical-tubular case; plural tumblers provided slidably within the key cylinder; a side bar which is provided slidably within the key cylinder, and approaches and moves away from the respective tumblers; and a lever member disposed so as to be able to rotate relative to the key cylinder, and connected to a lock device which is a mechanism to be operated.
In the above-described lock device, when a proper key, at which proper engaged portions are provided is inserted into the key cylinder, the plural tumblers engage respectively with the engaged portions provided at the key and slide to predetermined proper positions, and the side bar contacts predetermined abutting positions of all of the tumblers and moves from a locking position to an unlocking position. Interlockingly therewith, the side bar engages with the lever member and connects the key cylinder to the lever member. The key cylinder and the lever member thereby become integral and able to rotate. Due to the key being rotated, the locking mechanism which is the object of the key operation can be operated by the key.
On the other hand, when a substitute for the key, such as a key of a shape different than the proper key, or a screwdriver, or the like (these will be referred to collectively hereinafter as “improper keys”) is inserted in the key cylinder, at least one of the tumblers does not slide to the proper position, and the side bar is maintained at the locking position. In this way, the side bar does not engage with the lever member, and the key cylinder is not connected to the lever member by the side bar. Therefore, even if the key cylinder is rotated via the key, torque is not transmitted to the lever member, and the locking mechanism which is the object of the key operation cannot be operated.
Namely, in the lock device disclosed in JP-A No. 5-59849, if a proper key having proper engaged portions is inserted into the key cylinder and all of the tumblers which engage respectively with the plural engaged portions at the proper key move to the proper positions, the locking mechanism can be unlocked by the proper key being rotated. However, in a case in which an improper key, which has improper engaged portions or at which engaged portions are not provided, is inserted into the key insertion hole, even if this improper key is forcibly rotated, due to the key cylinder rotating idly with respect to the lever member, the locking mechanism is not unlocked. Further, because excessive force is not applied to the respective structural parts, breakage of the structural parts is prevented.
However, in a lock device such as that described above, at the time of unlocking, the key (the proper key) must be rotated against the rotation resistance of the key cylinder and the lever member, the operation resistance of the locking mechanism, and the like, and the torque which is transmitted from the key to the key cylinder is quite large. Accordingly, in order to reliably prevent deformation of the key, the strength along the twisting direction of the key must be made to be sufficiently large. For this reason, the material of a key used in a lock device such as described above is limited to a material having relatively high strength, such as iron, stainless steel, or the like. Further, the thickness of the key must be made to be sufficiently thick in accordance with the magnitude of the transmitted torque.
In order to reduce the strength along the twisting direction which is required of the key small, a lock device has been conceived of which carries out unlocking by, rather than rotating a key which is inserted in a key insertion hole of the lock device, pushing the key. However, among lock devices which operate a locking mechanism by a pushing movement, there have not been any which can effectively prevent breakage of the structural parts even if an improper key is inserted into the key insertion hole and excessive force is applied via this improper key.